1. Field of the Invention
The present invention relates to a shower head for supplying at least two kinds of reaction gases, which can react with each other, into a process chamber, and a film forming apparatus using the shower head.
2. Description of the Related Art
A process for forming a film is utilized for arranging a semiconductor integrated circuit on a semiconductor wafer or an LCD substrate. As a film to be formed, there is an oxide film for insulation or a metal film for wiring. In a case where a titanium or titanium nitride film as the metal film is formed, an organic metal compound, such as dimethylaminotitanium or diethylaminotitanium is used as a raw gas. These organic metal compounds are in a liquid state or phase at a room temperature and have a low vapor pressure, and thus require a strict temperature administration. For example, if such compounds are used as a process gas, it is necessary to provide the supply system with a vaporizing mechanism and a heating mechanism.
FIG. 15 is a cross sectional view schematically showing a conventional film forming apparatus. This exemplifies a CVD apparatus for forming a titanium nitride film, i.e., TiN film formed as a metal film, in which semiconductor wafers are processed one by one. In a case where a TiN film is formed, used reaction gases are, e.g., tetradiethylaminotitanium, i.e., TDEAT, gas used as a raw gas, and ammonia, i.e., NH.sub.3, gas used as a reduction gas.
As shown in FIG. 15, a work table 4 made of, e.g., graphite is arranged in a cylindrical process chamber 2 made of, e.g., aluminum. A semiconductor wafer W as an object to be processed is mounted and held on the work table 4. A transparent window 6 made of quartz glass is arranged at the bottom of the process chamber 2 to form a airtight seal. An intense heater, or heating lamps 8, such as halogen lamps, are rotatably arranged under the transparent window 6. The wafer W held on the work table 4 is heated by the heating lamps 8, up to a predetermined process temperature, such as 400.degree. C.
A shower head 10 for spreading and supplying a process gas into the process chamber 2 is arranged at the top of the process chamber 2. The shower head 10 includes a cylindrical shower head body 12 made of, e.g., aluminum and a plurality of diffusion plates, for example, two diffusion plates 14 arranged in the head body 12. Gas pipes 16 and 18 are connected to the shower head body 12 for supplying reaction gases, more specifically for supplying tetradiethylaminotitanium, i.e., TDEAT, gas, and ammonia, i.e., NH.sub.3, gas, respectively. The reaction gases are fed to the shower head body 12 through the gas pipes 16 and 18, respectively, along with a carrier gas consisting of an inactive gas, such as N.sub.2 gas. The two reaction gases are mixed in the shower head body 12, distributed through distribution holes 20 formed in the diffusion plates 14, and then spread through spreading holes 22 into the process space. A film forming material is provided by reaction of the two reaction gases, so that a TiN film is formed on the wafer surface.
TDEAT is in a liquid state or phase at a room temperature, such as 40.degree. C., or less, without reference to the pressure therearound. For this reason, the supply passage from a TDEAT source to the shower head 10 is heated not to liquefy the TDEAT gas in the passage.
On the other hand, where TDEAT is mixed with NH.sub.3 and heated at a temperature of about 100.degree. C. or more, it reacts with NH.sub.3 and causes a product to be deposited on, e.g., a metal surface. For example, if the TDEAT gas is overheated in the supply passage and mixed with the NH.sub.3 gas, the gases immediately start reacting. As a result, this gives rise to a problem in that a great amount of a product 24 is deposited in the shower head body 12.